Electrode assembly having improved flexural rigidity, method for preparing same, and electrochemical battery comprising same

ABSTRACT

The present invention relates to an electrode assembly, a method for preparing the same, and an electrochemical battery including the same, wherein the electrode assembly comprises: a cathode including a cathode active material and a cathode current collector; an anode including an anode active material and an anode current collector; and a separator interposed between the cathode and the anode. The electrode assembly has a flexural rigidity of 15 kgf/cm 2  or more when pressed using a pressure of 1 kgf/cm 2  to 30 kgf/cm 2  for 1 second to 15 seconds at 20 ° C. to 110 ° C.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Applications No. 10-2013-0142324, filed on Nov. 21, 2013,No. 10-2014-0041124, filed on Apr. 7, 2014, and No. 10-2014-0133339,filed on Oct. 2, 2014, in the Korean Intellectual Property Office areincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode assembly with improvedflexural rigidity in a battery, a method of preparing the same, and anelectrochemical battery including the same.

2. Description of the Related Art

In general, as a portable electronic device such as a video camera, acell phone, and a portable computer is lightened and conducts highperformance, research on a secondary battery as a power source for theportable electronic device is actively being made. This secondarybattery may include, for example, a nickel-cadmium battery, anickel-hydrogen battery, a nickel-zinc battery, a lithium secondarybattery, and the like. Among these batteries, the lithium secondarybattery may be down-sized and enlarged and also has an advantage of ahigh voltage and high energy density per unit weight and thus is used inmany fields.

This lithium secondary battery includes an electrode assembly as a mainconstituent element. However, in a process of manufacturing theelectrode assembly by disposing an enlarged separator between electrodesand pressing them, since the separator wound between the electrodes mayeasily escape therefrom due to an area and/or weight increase accordingto enlargement of the separator, adherence of the separator to theelectrodes needs to be increased. In addition, the electrode assemblyrequires excellent shape stability in order to prevent a shape changesuch as deformation of a battery and the like due to continuous chargesand discharges.

In order to improve adherence of the separator to the electrodes andheat resistance of the separator, a method of forming anorganic/inorganic mixed coating layer on one surface or both surfaces ofthe base film of the separator has been known (Korean RegistrationPatent No. 10-0775310) but may not sufficiently secure desired adherenceand thus not be uniformly applied to variously-sized and-shapedseparators.

Accordingly, development of an electrode assembly including a separatorhaving adherence applicable to an enlarged electrochemical battery andthus capable of improving shape stability of the battery is required.

SUMMARY OF THE INVENTION Technical Object

The present invention is to provide an electrode assembly havingimproved adherence between an electrode and a separator in an electrodeassembly and improved shape stability, and an electrochemical batteryusing the same.

Technical Solution

According to an example embodiment of the present invention, anelectrode assembly includes a cathode on which a positive activematerial is coated, an anode on which an anode active material iscoated, and a separator between the cathode and the anode, wherein theelectrode assembly has a flexural rigidity of greater than or equal to15 kgf/cm² when being compressed at 20° C. to 110° C. for 1 second to 15seconds, with a pressure of 1 kgf/cm² to 30 kgf/cm². According toanother example embodiment of the present invention, an electrochemicalbattery, particularly a lithium secondary battery includes the electrodeassembly according to the example embodiment.

Advantageous Effect

In an electrode assembly according to example embodiments of the presentinvention, adherence between an electrode and a separator of theelectrode assembly is improved. Accordingly, in a process ofmanufacturing the electrode assembly, the separator may be preventedfrom an escape and thus decrease a process inferiority rate and bestored for a long time.

In addition, the electrode assembly according to example embodiments ofthe present invention has excellent shape stability and may be minimizedfrom a shape change despite charges and discharges repeated for a longtime. Accordingly, a battery manufactured by using the electrodeassembly may have highly efficient charge and discharge characteristicsand be prevented from deterioration of battery performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the internal part of anelectrode assembly according to one example embodiment of the presentinvention, and the electrode assembly includes a cathode 6 having apositive active material layer 5 on a cathode current collector 4; ananode 12 having a negative active material layer 12 on an anode currentcollector 11; and a separator 9 disposed between the cathode 6 and theanode 12 and respectively adhered to the cathode or the anode, andincluding a porous substrate 8 and porous adhesive layers 7 and 7′ onboth surfaces of the porous substrate.

FIG. 2 is a cross-sectional view showing the internal part of anelectrode assembly according to another example embodiment of thepresent invention, and the electrode assembly includes the cathode 6having the positive active material layer 5 on the cathode currentcollector 4; the anode 12 having the negative active material layer 10on the anode current collector 11; and the separator 9 disposed betweenthe cathode 6 and the anode 12 and respectively adhered to the cathodeor the anode, and including the porous substrate 8 and the porousadhesive layer 7 on one surface of the porous substrate.

DETAILED DESCRIPTION

Hereinafter, the present invention is described in detail. Thedisclosures that are not described in the present specification may befully recognized and by conveyed by those skilled in the art in atechnical or similar field of the present invention and thus are omittedherein.

Hereinafter, referring to FIG. 1, an electrode assembly according to anexample embodiment of the present invention is described. According toan example embodiment of the present invention, an electrode assemblyincludes a cathode including a positive active material and a cathodecurrent collector, an anode including an anode active material and aanode current collector, and a separator disposed between the cathodeand the anode, wherein the electrode assembly has a flexural rigidity ofgreater than or equal to 15 kgf/cm² when being compressed at 20° C. to110° C. for 1 second to 15 seconds, with a pressure of 1 kgf/cm² to 30kgf/cm².

The flexural rigidity of greater than or equal to 15 kgf/cm² when beingcompressed at 20° C. to 110° C. for 1 second to 15 seconds, with apressure of 1 kgf/cm² to 30 kgf/cm² has a relation with a shapestability of the electrode assembly. This electrode assembly mayminimize a battery shape change such as battery deformation and the likedespite continuous charges and discharges for a long time and thusrealize highly efficient charge and discharge characteristics andprevent deterioration of battery performance. The flexural rigidity maybe measured using a 3 point bending machine (ex. UTM) according to ASTMD790, but is not limited thereto. The flexural rigidity may bespecifically 17 kgf/cm² to 50 kgf/cm², and more specifically 20 kgf/cm²to 30 kgf/cm².

Referring to FIG. 1, the electrode assembly according to the embodimentincludes a cathode 6 including a positive active material layer 5 on acathode current collector 4; an anode 12 including an anode activematerial layer 10 formed on a anode current collector 11; and aseparator 9 disposed between the cathode 6 and the anode 12 andrespectively attached to the cathode or the anode. The separator 9 mayinclude a porous substrate 8 and porous adhesive layers 7 and 7′ on bothsurfaces of the porous substrate 8.

The porous substrate 8 may have a plurality of pore and may generally bea porous substrate used in an electrochemical device. Non-limitingexamples of the porous substrate 8 may be a polymer film formed of apolymer or a mixture of two or more of polyethylene, polypropylene,polyethyleneterephthalate, polybutyleneterephthalate, polyester,polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone,polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole,polyethersulfone, polyphenyleneoxide, a cyclic olefin copolymer,polyphenylenesulfide, and polyethylenenaphthalene. For example, theporous substrate 8 may be a polyolefin-based substrate, and thepolyolefin-based substrate may improve has safety of a battery due toits improved shut-down function. The polyolefin-based substrate may be,for example, selected from a polyethylene single film, a polypropylenesingle film, a polyethylene/polypropylene double film, apolypropylene/polyethylene/polypropylene triple film, and apolyethylene/polypropylene/polyethylene triple film. For anotherexample, the polyolefin-based resin may include a non-olefin resin inaddition to an olefin resin or a copolymer of olefin and a non-olefinmonomer.

A thickness of the porous substrate 8 may be 1 μm to 40 μm, for example5 μm to 15 μm. Within the thickness range, a separator may have adesirable thickness that is thick to prevent a short-circuit between thecathode and the anode of a battery and is also not thick to increaseinternal resistance.

The porous adhesive layers 7 and 7′ may be formed on both surfaces ofthe porous substrate 8, and may be formed of a porous adhesive layercomposition. The porous adhesive layer composition may include anorganic binder and a solvent.

The organic binder may be an acryl-based copolymer, for example aacryl-based copolymer including a (meth)acrylate-based monomer-derivedrepeating unit. In addition, the acryl-based copolymer may furtherinclude an acetate group-containing monomer-derived repeating unit inaddition to the (meth)acrylate-based monomer-derived repeating unit.When the acryl-based copolymer having a (meth)acrylate-basedmonomer-derived repeating unit and/or acetate group-containingmonomer-derived repeating unit is used as a binder, a separator may bestrongly adhered to a cathode or an anode in a secondary batteryenvironment wherein the separator is actually used and thus be preventedfrom an escape during an electrode assembly process, decrease a processinferiority rate, and realize a long term storage. In addition, theporous adhesive layer retains an electrolyte solution and thus maymaintain satisfactory ion conductivity between the electrodes and notdeteriorate a porosity of the porous substrate.

A glass transition temperature (Tg) of the acryl-based copolymer may beless than 100° C., for example, 20° C. to 60° C., specifically 30° C. to45° C. Within the ranges, it is advantageous for good adherence and thusensuring shape stability at a temperature where a separator is disposedbetween electrodes followed by being compressed.

The acryl-based copolymer having a (meth)acrylate-based monomer-derivedrepeating unit and/or an acetate group-containing monomer-derivedrepeating unit used in an example embodiment of the present invention isnot particularly limited as long as it provides good adherence at acompression temperature between the cathode and the anode, and forexample, the acryl-based copolymer may be a copolymer by polymerizing atleast one (meth)acrylate-based monomer selected from the groupconsisting of butyl(meth)acrylate, propyl(meth)acrylate,ethyl(meth)acrylate and methyl(meth)acrylate. Or, the acryl-basedcopolymer may be a copolymer of at least one (meth)acrylate-basedmonomer selected from the group consisting of butyl (meth)acrylate,propyl (meth)acrylate, ethyl (meth)acrylate, and methyl (meth)acrylateand an acetate group-containing monomer selected from the groupconsisting of vinyl acetate and allyl acetate.

The acetate group-containing monomer-derived repeating unit may be arepeating unit of Chemical Formula 1:

In Chemical Formula 1, R₁ is a single bond or a linear or branched C1 toC6 alkyl, R₂ is hydrogen or methyl, and l is an integer of 1 to 100.

For example, the acetate group-containing monomer-derived repeating unitmay be an acetate group-containing monomer-derived repeating unitselected from the group consisting of vinyl acetate and allyl acetate.The acryl-based copolymer may be prepared by polymerizing(meth)acrylate-based monomers or a (meth)acrylate-based monomer andother monomer in addition to the (meth)acrylate-based monomers. Forexample, the other monomer may be an acetate group-containing monomer.In this case, a (meth)acrylate-based monomer and another monomer,specifically, an acetate group-containing monomer may be polymerized ina mole ratio of 3:7 to 7:3, specifically 4:6 to 6:4, and morespecifically about 5:5. The acryl-based copolymer may be, for example,prepared through a polymerization reaction of a butyl (meth)acrylatemonomer, a methyl (meth)acrylate monomer, and a vinyl acetate and/orallyl acetate monomer in a mole ratio of 3 to 5:0.5 to 1.5:4 to 6,specifically, 4:1:5.

In an example embodiment of the present invention, the porous adhesivelayer composition may further include an inorganic particle.

The inorganic particle used in an example embodiment of the presentinvention is not particularly limited, and may be an inorganic particlethat is generally in this filed. Non-limiting examples of the inorganicparticle used in the example embodiment of the present invention may beAl₂O₃, SiO₂, B₂O₃, Ga₂O₃, TiO₂, or SnO₂. These may be used alone or in amixture of two or more. The inorganic particle used in the exampleembodiment of the present invention may be, for example, Al₂O₃(alumina). A size of the inorganic particle used in the exampleembodiment of the present invention is not particularly limited, and itsaverage particle diameter may be 1 nm to 2,000 nm, for example, 100 nmto 1,000 nm, 300 nm to 500 nm. When the inorganic particle having thesize within the ranges, dispersibility of the inorganic particle in theporous adhesive layer composition and formation processibility of aporous adhesive layer may be prevented from being deteriorated, athickness of the porous adhesive layer may be appropriately controlledand thus reduction of mechanical properties and increase of electricalresistance may be prevented. In addition, sizes of pores generated inthe separator are appropriately controlled and thus internal apossibility of short-circuit may be reduced during charge and dischargeof a battery. In the porous adhesive layer composition, the inorganicparticle may be used in a form of inorganic dispersion liquid includingthe inorganic particle in an appropriate solvent.

The appropriate solvent is not particularly limited, and may be ageneral solvent in this art. The appropriate solvent to disperse theinorganic particle may be, for example, acetone. The inorganicdispersion liquid may be prepared by a general method without particularlimitation, and may be prepared, for example by adding Al₂O₃ in acetonein an appropriate amount, and milling the same using beads mill todisperse it.

In the porous adhesive layer, the inorganic particle may be included inan amount of 70 wt % to 95 wt %, specifically 75 wt % to 90 wt %, andmore specifically 80 wt % to 90 wt % based on the total weight of theporous adhesive layer. When the inorganic particle is included withinthe range, heat dissipation properties of the inorganic particle may besufficiently realized, and thermal shrinkage of the separator may beeffectively suppressed when a porous adhesive layer is formed on aporous substrate using the same.

Non-limiting example of the solvent used in an example embodiment of thepresent invention may be acetone, dimethyl formamide, acetone,dimethylsulfoxide, dimethyl acetamide, dimethylcarbonate, orN-methylpyrrolidone. A content of the solvent may be 20 wt % to 99 wt %,specifically 50 wt % to 95 wt %, and more specifically 70 wt % to 95 wt% based on a weight of the porous adhesive layer composition. When thesolvent is included within the range, a porous adhesive layercomposition may be easily prepared and a drying process of a porousadhesive layer may be easily performed.

Thicknesses of the porous adhesive layers 7 and 7′ may be 1 μm to 15 μm,specifically 1 μm to 10 μm, more specifically 1 μm to 8 μm, or 1 μm to 5μm. When the porous adhesive layer has a thickness within the thicknessrange, excellent thermal stability and adherence may be obtained due toa porous adhesive layer having an appropriate thickness, and internalresistance of a battery is suppressed from being increase by preventingan entire thickness of a separator from being extremely thick.

The electrode assembly according to the present example embodiment mayhave a compression thickness variation ratio of greater than or equal to10% according to Equation 1.

Compression thickness variation ratio (%)=[(Thickness of an electrodeassembly compressed at 20° C.−Thickness of the electrode assemblycompressed at 100° C.)/Thickness of the electrode assembly compressed at20° C]×100   [Equation 1]

In Equation 1, the thickness of an electrode assembly compressed at 20°C. is a thickness of a central portion of an electrode assemblyincluding a stacked cathode/separator/anode after compressing it at 20°C. for 1 to 10 seconds, with a pressure of 1 to 30 kgf/cm² and measuringthe thickness in one 1 hour, and the thickness of an electrode assemblycompressed at 100° C. is a thickness of a central portion of theelectrode assembly for 1 to 10 seconds, with a pressure of 1 to 30kgf/cm² and measuring the thickness in one 1 hour. When the compressionthickness variation ratio is within the range, the separator may beprevented from an escape in the electrode assembly due to excellentadherence during compression of the electrodes and the separator at ahigh temperature (ex. 100° C.) and thus deteriorate a processinferiority rate and accomplish a long term storage. The compressionthickness variation ratio may be specifically greater than or equal to13% and less than 50%, specifically, greater than or equal to 15% andless than 47%, and more specifically, greater than or equal to 20% andless than 45%. As the compression thickness variation ratio is larger,adherence of the separator to the cathode or the anode may be moreimproved.

Hereinafter, referring to FIG. 2, another electrode assembly accordingto another example embodiment of the present invention is described.Referring to FIG. 2, an electrode assembly according to another exampleembodiment of the present invention includes a cathode 6 including apositive active material layer 5 formed on a cathode current collector4; an anode 12 including an anode active material layer 10 formed on aanode current collector 11; and a separator 9 disposed between thecathode 6 and the anode 12 and attached to the cathode or the anode. Theseparator 9 may include a porous substrate 8 and a porous adhesive layer7 formed on one surface of the porous substrate 8. The electrodeassembly according to the present example embodiment has substantiallythe same constituent elements as those of the electrode assemblyaccording to the example embodiment of the present invention except forforming the porous adhesive layer 7 not on both surfaces but only on onesurface of the porous substrate 8 of the separator 9 and thus will notbe described in detail.

The electrode assembly may have a flexural rigidity of greater than orequal to 15 kgf/cm², for example, 17 kgf/cm² to 50 kgf/cm², specifically20 kgf/cm² to 30 kgf/cm² when being compressed at 20° C. to 110° C. for1 second to 15 seconds, with a pressure of 1 kgf/cm² to 30 kgf/cm². Inother words, even when the porous adhesive layer 7 is formed only on onesurface of the porous substrate 8, sufficient adherence to an electrode(a cathode or an anode) is obtained, and a battery shape change may beminimized despite continuous charges and discharges.

Hereinafter, an electrode assembly according to another exampleembodiment of the present invention is described. The electrode assemblyaccording to the present embodiment may additionally include a differentkind of organic binder other than the acryl-based copolymer as anorganic binder in the porous adhesive layer. This electrode assembly issubstantially the same as the electrode assemblies according to theabove example embodiment of the present invention or another exampleembodiment of the present invention except for additionally adding theorganic binder to the porous adhesive layer. Accordingly, theadditionally added binder other than the acryl-based copolymer may bemainly described hereinafter. The addition of the binder in the presentexample embodiment may further improve adherence and heat resistance.

Examples of an additional binder in addition to acryl-based copolymermay be one or mixture thereof selected from a polyvinylidene fluoride(PVdF) homopolymer, a polyvinylidene fluoride-hexafluoropropylenecopolymer (PVdF-HFP), polymethylmethacrylate, polyacrylonitrile,polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, celluloseacetate, cellulose acetate butyrate, cellulose acetate propionate,cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose,cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and anacrylonitrile styrene butadiene copolymer. More specifically, apolyvinylidene fluoride-based binder may be used and examples thereofmay be a polyvinylidene fluoride (PVDF) homopolymer, polyvinylidenefluoride-hexafluoropropylene (PVDF-HFP), polyvinylidenefluoride-trichloroethylene (PVDF-TCE), polyvinylidenefluoride-chlorotrifluoroethylene (PVDF-CTFE), and the like.

A weight ratio of the acryl-based copolymer and the additional bindermay be 9.9:0.1 to 2.5:7.5. Specifically, it may be 9.9:0.1 to 5:5 andmore specifically, 9:1 to 5.5:4.5, or 8:2 to 6:4. Within the range, theseparator may provide an electrode assembly having excellent shapestability as well as maintaining sufficient adherence. Accordingly, theelectrode assembly may prevent performance deterioration of a battery,and the battery may have highly efficient charge and dischargecharacteristics.

When the PVdF-based binder is further included, the PVdF-based bindermay have a weight average molecular weight (Mw) of 500,000 to 1,500,000(g/mol). For specific example, the PVdF-based binder may have a weightaverage molecular weight (Mw) of 1,000,000 to 1,500,000 (g/mol). Foranother example, two or more binders having different weight averagemolecular weights may be mixed. For example, a binder having a weightaverage molecular weight of less than or equal to 1,000,000 g/mol and abinder having a weight average molecular weight of greater than or equalto 1,000,000 g/mol may be mixed. When the PVdF-based binder having themolecular weight within the range is used, adherence between the porousadhesive layer and the porous substrate is fortified, a porous substratethat is weak against heat may be effectively prevented from beingcontracted, a separator having sufficiently improved electrolyteimpregnation properties may be prepared, and a battery effectivelygenerating electrical output may be manufactured.

Hereinafter, a method of preparing an electrode assembly according to anexample embodiment of the present invention is described. The method ofpreparing an electrode assembly according to an example embodiment ofthe present invention may include manufacturing a cathode by forming acathode active material layer on a cathode current collector,manufacturing an anode by forming an anode active material layer on ananode current collector, and disposing the separator according to thepresent invention between the cathode and the anode.

According to another example embodiment of the present invention, amethod of preparing an electrode assembly may additionally includecompressing a structure of the cathode/the separator/the anode at 20° C.to 110° C. for 1 second to 10 seconds with a pressure of 1 kgf/cm² to 30kgf/cm² after disposing the separator between the cathode and the anode.When the separator manufactured in the above method is compressed withthe cathode and the anode at 20° C. to 110° C. for 1 second to 10seconds with a pressure of 1 kgf/cm² to 30 kgf/cm² after disposing theseparator between the cathode and the anode, the acryl-based copolymerof the present invention may form strong adherence of the separator tothe cathode or the anode and improve shape storage stability of theelectrode assembly. The compression may be performed at a temperaturedetermined considering a temperature where the porous substrate of theseparator is not remarkably thermally shrunk and a temperature where theporous adhesive layer of the separator is adhered and specifically, atroom temperature or 80° C. to 100° C. for 1 second to 5 seconds with apressure of 5 kgf/cm² to 10 kgf/cm².

In addition, a method of manufacturing an electrode assembly accordingto still another example embodiment of the present invention mayadditionally include secondarily compressing the electrode assembly at60° C. to 110° C. for 30 seconds to 180 seconds with a pressure of 1kgf/cm² to 30 kgf/cm² after disposing the separator between cathode andanode, primarily compressing the electrode assembly at 20° C. to 110° C.for 1 second to 10 seconds with a pressure of 1 kgf/cm² to 30 kgf/cm²,housing it in a battery case, and injecting an electrolyte solution intoa battery case. Herein, the battery case may be an aluminum pouch, andthe like but is not limited thereto.

In addition, a method of manufacturing an electrode assembly accordingto still another example embodiment of the present invention mayadditionally include storing the electrode assembly for 6 hours to 48hours at 10° C. to 30° C. after injecting the electrolyte solution andbefore secondarily compressing the electrode assembly. The secondarycompression may form stronger adherence of the acryl-based copolymer ofthe present invention to the cathode or the anode and improve shapestorage stability of the electrode assembly.

The cathode includes include a cathode current collector and a positiveactive material layer formed on the cathode current collector. Thepositive active material layer includes a positive active material, abinder, and optionally a conductive material. The cathode currentcollector may use aluminum (Al), nickel (Ni), and the like, but is notlimited thereto. The positive active material may use a compound beingcapable of intercalating and deintercalating lithium. Specifically atleast one of a composite oxide or a composite phosphate of a metalselected from cobalt, manganese, nickel, aluminum, iron, or acombination thereof and lithium may be used. More specifically, thepositive active material may use lithium cobalt oxide, lithium nickeloxide, lithium manganese oxide, lithium nickel cobalt manganese oxide,lithium nickel cobalt aluminum oxide, lithium iron phosphate, or acombination thereof. The binder improves binding properties of positiveactive material particles with one another and with a current collector,and specific examples may be polyvinyl alcohol, carboxylmethylcellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, and the like, but arenot limited thereto. These may be used alone or as a mixture of two ormore. The conductive material improves conductivity of an electrode andexamples thereof may be natural graphite, artificial graphite, carbonblack, a carbon fiber, a metal powder, a metal fiber, and the like, butare not limited thereto. These may be used alone or as a mixture of twoor more. The metal powder and the metal fiber may use a metal of copper,nickel, aluminum, silver, and the like.

The anode includes a anode current collector and an anode activematerial layer formed on the anode current collector. The anode currentcollector may use copper (Cu), gold (Au), nickel (Ni), a copper alloy,and the like, but is not limited thereto. The anode active materiallayer may include an anode active material, a binder and optionally aconductive material. The anode active material may be a material thatreversibly intercalates/deintercalates lithium ions, a lithium metal, alithium metal alloy, a material being capable of doping and dedopinglithium, a transition metal oxide, or a combination thereof. Thematerial that reversibly intercalates/deintercalates lithium ions may bea carbon material which is any generally-used carbon-based anode activematerial, and examples thereof may be crystalline carbon, amorphouscarbon, or a combination thereof. Examples of the crystalline carbon maybe graphite such as amorphous shape, plate shape, flake shape, sphericalshape or fiber shape natural graphite or artificial graphite. Examplesof the amorphous carbon may be soft carbon or hard carbon, a mesophasepitch carbonized product, fired coke, and the like. The lithium metalalloy may be an alloy of lithium and a metal selected from Na, K, Rb,Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Thematerial being capable of doping and dedoping lithium may be Si, SiO_(x)(0<x<2), a Si—C composite, a Si—Y alloy, Sn, SnO₂, a Sn—C composite, aSn—Y, and the like, and at least one of these may be mixed with SiO₂.Specific examples of the element Y may be selected from Mg, Ca, Sr, Ba,Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe,Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In,Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a combination thereof. Thetransition metal oxide may be vanadium oxide, lithium vanadium oxide,and the like. The binder and the conductive material used in the anodemay be the same as the binder and conductive material of the cathode.

The cathode and the anode may be manufactured by mixing each activematerial composition including each active material and a binder, andoptionally a conductive material in a solvent, and coating the activematerial composition on each current collector. Herein, the solvent maybe N-methylpyrrolidone, and the like, but is not limited thereto.

The electrolyte solution may include a salt having a structure of A⁺B⁻dissolved or dissociated in an organic solvent.

The organic solvent serves as a medium for transmitting ions taking partin the electrochemical reaction of a battery. Specific examples thereofmay be selected from a carbonate-based solvent, an ester-based solvent,an ether-based solvent, a ketone-based solvent, an alcohol-basedsolvent, and an aprotic solvent. Examples of the carbonate-based solventmay be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropylcarbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate(EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylenecarbonate (PC), butylene carbonate (BC), and the like. Particularly,when the linear carbonate compounds and cyclic carbonate compounds aremixed, an organic solvent having a high dielectric constant and a lowviscosity may be provided. The cyclic carbonate compound and the linearcarbonate compound are mixed together in a volume ratio ranging from 1:1to 1:9. Examples of the ester-based solvent may be methylacetate,ethylacetate, n-propylacetate, dimethylacetate, methylpropionate,ethylpropionate, γ-butyrolactone, decanolide, valerolactone,mevalonolactone, caprolactone, and the like. Examples of the ether-basedsolvent may be dibutylether, tetraglyme, diglyme, dimethoxyethane,2-methyltetrahydrofuran, tetrahydrofuran, and the like. Examples of theketone-based solvent may be cyclohexanone, and the like, and examples ofthe alcohol-based solvent may be ethanol, isopropyl alcohol, and thelike. The organic solvent may be used singularly or in a mixture of twoor more, and when the organic solvent is used in a mixture of two ormore, the mixture ratio may be controlled in accordance with a desirablecell performance.

Non-limiting examples of the A⁺ may be a cation of an alkali metalcation such as Li⁺, Na⁺, or K⁺, or a combination thereof. Non-limitingexamples of the B⁻ may be an anion of PF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, AlO₂ ⁻,Cl⁻, Br⁻, I⁻, ClO₄ ⁻, AsF₆ ⁻, B(C₂O₄)₂ ⁻, CH₃CO₂ ⁻, N(SO₃C₂F₅)₂ ⁻,C₄F₉SO₃ ⁻, CF₃SO₃ ⁻, N(CF₃SO₂)₂ ⁻, or C(CF₂SO₂)₃ ⁻, or a combinationthereof. For example, a lithium salt may be used, and the lithium saltsupplies lithium ions in a battery, basically operates anelectrochemical battery, and improves lithium ion transportation betweenpositive and anodes therein. Examples of the lithium salt may be LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₃C₂F₅)₂, LiN(CF₃SO₂)₂, LiC₄F₉SO₃, LiClO₄,LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂), x and y arenatural numbers, LiCl, LiI, LiB(C₂O₄)₂, or a combination thereof. Thelithium salt may be used in a concentration ranging from 0.1 M to 2.0 M.When the lithium salt is included within the above concentration range,an electrolyte may have excellent performance and lithium ion mobilitydue to optimal electrolyte conductivity and viscosity.

The electrochemical battery according to an example embodiment of thepresent invention may be specifically a lithium secondary battery suchas a lithium metal secondary battery, a lithium ion secondary battery, alithium polymer secondary battery, or a lithium ion polymer secondarybattery.

DETAILED DESCRIPTION

Hereinafter, Examples, Comparative Examples and Experimental Examplesare provided in order to illustrate the present invention in detail.However, the following Examples, Comparative Examples, and ExperimentalExamples are examples of the present invention and are not to beconstrued as limiting the present invention.

PREPARATION EXAMPLE Preparation Example 1 Preparation of Separator

A first binder solution was prepared by polymerizing butyl methacrylate(BMA), methyl methacrylate (MMA), and vinyl acetate (VAc) in a moleratio of 4/1/5 to obtain an acryl-based copolymer binder (Tg: 35° C.,Mw: 600K (GPC)), dissolving the acryl-based copolymer binder in a solidamount of 10 wt % in acetone, and stirring the solution with an agitatorat 40° C. for 2 hours. On the other hand, an alumina dispersion liquidwas prepared by adding alumina (LS235, Nippon Light Metal Co., Ltd.) inan amount of 25 wt % to acetone and dispersing it therein at 25° C. for2 hours with a bead mill. The first binder solution and the aluminadispersion liquid were mixed in 1/5 of a ratio between the binder solidand alumina solid, and acetone was added to the mixture to be an entiresolid of 10 wt %, preparing a porous adhesive layer composition. Theporous adhesive layer composition was coated to be respectively 2 μmthick on both surfaces of a 12 μm-thick polyethylene fabric panel (Wscope) to manufacture a separator having a total thickness of 16 μm.

Preparation Example 2 Preparation of Separator

A first binder solution was prepared by polymerizing butyl methacrylate(BMA), methyl methacrylate (MMA), and vinyl acetate (VAc) in a moleratio of 4/1/5 to prepare an acryl-based copolymer binder (Tg: 35° C.,Mw: 600K (GPC)), dissolving the acryl-based copolymer binder in a solidamount of 10 wt % in acetone, and stirring the solution with an agitatorat 40° C. for 2 hours. A second binder solution was prepared bydissolving KF9300 (Kureha Corp., Mw: 1,200,000 g/mol) as a PVdF-basedbinder in a solid amount of 7 wt % in a mixed solvent of acetone andDMAc and stirring the solution at 40° C. for 4 hours with an agitator.On the other hand, an alumina dispersion liquid was prepared by addingalumina (LS235, Nippon Light Metal Co., Ltd.) in an amount of 25 wt % inacetone and dispersing it therein at 25° C. for 2 hours with a beadmill. The first and second binder solutions and the alumina dispersionliquid were mixed to have 8/2 of a weight ratio between the acryl-basedbinder and the PVdF-based binder and 1/5 of a ratio between the bindersolid and the alumina solid, and acetone was added thereto to prepare aporous adhesive layer composition to have an entire solid of 10 wt %.The porous adhesive layer composition was coated to be respectively on 2μm thick both surfaces of a 12 μm-thick polyethylene fabric panel (Wscope), manufacturing a separator having a total thickness of 16 μm.

Preparation Example 3 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for using the acryl-based binder and the PVdF-basedbinder in a weight ratio of 7/3.

Preparation Example 4 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for using the acryl-based binder and the PVdF-basedbinder in a weight ratio of 6/4.

Preparation Example 5 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for using the acryl-based binder and the PVdF-basedbinder in a weight ratio of 3/7.

Preparation Example 6 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 1 except for coating the porous adhesive layer composition to be2 μm thick on one surface of a polyethylene fabric panel to have thetotal thickness of the separator of 14 μm.

Comparative Preparation Example 1 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for mixing the acryl-based binder and the PVdF-basedbinder in a weight ratio of 1/9.

Comparative Preparation Example 2 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for mixing the acryl-based binder and the PVdF-basedbinder in a weight ratio of 0.5/9.5.

Comparative Preparation Example 3 Preparation of Separator

A separator was manufactured according to the same method as PreparationExample 2 except for using only the PVdF-based binder.

Each binder composition of the separators according to PreparationExamples 1 to 6 and Comparative Preparation Examples 1 to 3 are providedin Table 1.

TABLE 1 Acryl-based PVdF-based binder binder Preparation Example 1 100 0Preparation Example 2 80 20 Preparation Example 3 70 30 PreparationExample 4 60 40 Preparation Example 5 30 70 Preparation Example 6 100 0Comparative Preparation Example 1 10 90 Comparative Preparation Example2 5 95 Comparative Preparation Example 3 0 100

EXAMPLES Example 1 Preparation of Electrode Assembly

A positive active material coating composition was prepared by using LCO(LiCoO₂) as a positive active material, PVdF (polyvinylidene fluoride)as a binder, and carbon black as a conductive agent. The positive activematerial coating composition was prepared by dispersing an activematerial, a binder, and a conductive material in a weight ratio of94:3:3 in N-methyl-2-pyrrolidone with a mixer (Planetary Despa Mixer)into slurry and coating the slurry to be 94 μm thick on both surfaces ofa 14 μm-thick aluminum foil with a doctor blade and drying it. Then, thecoated foil was pressed with a roll presser and dried with a vacuumdryer to remove moisture in a coating layer, manufacturing a cathode. Onthe other hand, an anode active material coating composition wasprepared by using graphite as an anode active material and SBR(styrene-butadiene rubber) and CMC (carboxy methyl cellulose) as abinder. Herein, the anode active material and the binder were used in aweight ratio of 96:4, and the SBR and the CMC were used in a weightratio of 1:1. Then, an anode was manufactured according to the samemethod as the cathode except for forming a 120 μm-thick coating layer onboth surfaces of a 8 μm-thick copper foil. The cathode and the anodewere respectively cut into a size of 100 cm×4.2 cm, and the separatoraccording to Preparation Example 1 was cut into a size of 100 cm×4.4 cmand then, disposed between the cathode and the anode and wound therewithinto a size 7 cm (a length direction)×4.4 cm (a width direction),manufacturing an electrode assembly.

Example 2 Preparation of Electrode Assembly

An electrode assembly according to Example 2 was manufactured accordingto the same method as Example 1 except for using the separator accordingto Preparation Example 2.

Example 3 Preparation of Electrode Assembly

An electrode assembly according to Example 3 was manufactured accordingto the same method as Example 1 except for using the separator accordingto Preparation Example 3.

Example 4 Preparation of Electrode Assembly

An electrode assembly according to Example 4 was manufactured accordingto the same method as Example 1 except for using the separator accordingto Preparation Example 4.

Example 5 Preparation of Electrode Assembly

An electrode assembly according to Example 5 was manufactured accordingto the same method as Example 1 except for using the separator accordingto Preparation Example 5.

Example 6 Preparation of Electrode Assembly

An electrode assembly according to Example 6 was manufactured accordingto the same method as Example 1 except for using the separator accordingto Preparation Example 6, positioning a cathode to face the surface ofthe separator having a porous adhesive layer and an anode to face theother surface of the separator having no porous adhesive layer.

Comparative Example 1 Preparation of Electrode Assembly

An electrode assembly according to Comparative Example 1 wasmanufactured according to the same method as Example 1 except for usingthe separator according to Comparative Preparation Example 1.

Comparative Example 2 Preparation of Electrode Assembly

An electrode assembly according to Comparative Example 2 wasmanufactured according to the same method as Example 1 except for usingthe separator according to Comparative Preparation Example 2.

Comparative Example 3 Preparation of Electrode Assembly

An electrode assembly according to Comparative Example 3 wasmanufactured according to the same method as Example 1 except for usingthe separator according to Comparative Preparation Example 3.

EXPERIMENTAL EXAMPLE

Each flexural rigidity and compression thickness variation ratio of theelectrode assemblies according to Examples 1 to 6 and ComparativeExamples 1 to 3 was measured in the following method, and the resultsare provided in Table 2.

Flexural Rigidity

The electrode assemblies according to Examples 1 to 6 and ComparativeExamples 1 to 3 were respectively compressed for 10 seconds under apressure of 9 kgf/cm² at 80° C., 90° C., 100° C., and 110° C.,respectively. Subsequently, flexural rigidity of each electrodeassemblies was put in an MD direction toward a right-left direction in adistance of 60 mm and measured according to ASTM D790 with a 3 pointbending machine (UTM), while dropped at a speed of 2.8 mm/min.

Compression Thickness Variation Ratio

Each electrode assembly according to Examples 1 to 6 and ComparativeExamples 1 to 3 was compressed at 20° C. under a pressure of 9 kgf/cm²for 3 seconds, and one hour later, its thickness in the middle wasmeasured with a 15 cm steel ruler. Each electrode assembly was alsocompressed at 100° C. under a pressure of 9 kgf/cm² for 10 seconds, andone hour later, its thickness in the middle was measured with a 15 cmsteel ruler. The thicknesses compressed at 20° C. and 100° C. were usedto calculate a compression thickness variation ratio through thefollowing formula.

A compression thickness variation ratio (%)=[(Thickness of an electrodeassembly compressed at 20° C.−Thickness of an electrode assemblycompressed at 100° C.)/Thickness of an electrode assembly compressed at20° C]×100

TABLE 2 Compression thickness Flexural rigidity (mm) and compressiondepending on a press thickness variation ratio (%) temperature (kgf/cm²)20° 100° 80° 90° 100° 110° C. C. Variation C. C. C. C. press press ratio(%) Example 1 43 47 50 50 6.5 5 23 Example 2 41 44 47 48 6.5 5 23Example 3 36 39 40 40 6.5 5 23 Example 4 17 20 23 24 6.5 5.5 15.38Example 5 15 20 23 25 6.5 5.5 15.38 Example 6 39 40 42 43 6.5 5 23Comparative 7 8 9 10 6.5 6.0 7.69 Example 1 Comparative 3 5 6 6 6.5 6.07.69 Example 2 Comparative (no flexural point, 6.5 6.0 7.69 Example 3non-measurable)

Thickness Variation Ratio after Cycles

The electrode assemblies according to Examples 2 and 3 and ComparativeExample 3 were manufactured in the following method, their thicknessvariation ratios after cycles were measured, and the results areprovided in Table 3.

Each electrode assembly according to Examples 2 and 3 and ComparativeExample 3 was compressed at 100° C. for 3 seconds under a pressure of 9kgf/cm² and put in an aluminum pouch, an electrolyte solution wasinjected thereinto, and the pouch was sealed. Herein, the electrolytesolution was prepared by dissolving 1.1 M LiPF₆ in 2.7 g of an organicsolvent of ethylene carbonate (EC)/ethylmethyl carbonate (EMC) in aEC:EMC volume ratio of 30/70. Then, the pouched electrode assembly wasstored at room temperature for 12 hours, compressed at 100° C. for 30seconds under a pressure of 9 kgf/cm², and then, stored at roomtemperature for 12 hours. Subsequently the pouched electrode assemblywas precharged under a condition of 0.2 C for one hour in acharge/discharger, and its thickness of the electrode assembly in themiddle was measured with a 15 cm steel ruler. Then, the pouch was opento remove gas, charge and discharge were 500 times repeated under acondition of 0.7 C, and the thickness of the electrode assembly in themiddle was measured.

TABLE 3 Thickness Thickness Thickness variation before pre- after 500ratio after charging (mm) cycles (mm) cycling (%) Example 2 3.0 3.5 16.7Example 3 3.0 3.5 16.7 Comparative Example 3 3.0 4.0 33.3

Referring to Tables 2 and 3, when an acryl-based copolymer was usedalone or mixed with the polyvinylidene fluoride-based binder in a weightratio of 9.9:0.1 to 2.5:7.5, a compression thickness variation ratio ofgreater than or equal to 10% and thus excellent adherence of electrodesto a separator was found. In addition, flexural rigidity of greater thanor equal to 15 kgf/cm² and thus excellent shape stability of anelectrode assembly was found.

Accordingly, a separator may be prevented from an escape and thus maydecrease an inferiority rate in an electrode assembly process andaccomplish a long time storage. The electrode assembly may have aminimized from a shape change during charges and discharges repeated fora long time. This is supported by a thickness variation ratio of lessthan or equal to 20% after cycles. Accordingly, a battery cell using theelectrode assembly may have highly efficient charge and dischargecharacteristics and be prevented from deterioration of batteryperformance.

What is claimed is:
 1. An electrode assembly comprising a cathodeincluding a positive active material and a cathode current collector, ananode including an anode active material and a anode current collector,and a separator disposed between the cathode and the anode, wherein theelectrode assembly has a flexural rigidity of greater than or equal to15 kgf/cm² when being compressed at 20° C. to 110° C. for 1 second to 15seconds, with a pressure of 1 kgf/cm² to 30 kgf/cm².
 2. The electrodeassembly of claim 1, wherein the separator comprises a porous substrateand a porous adhesive layer disposed on one surface or both surfaces ofthe porous substrate and including an acryl-based copolymer includinga(meth)acrylate-based monomer-derived repeating unit.
 3. The electrodeassembly of claim 2, wherein the acryl-based copolymer further comprisesan acetate group-containing monomer-derived repeating unit.
 4. Theelectrode assembly of claim 2, wherein the (meth)acrylate-basedmonomer-derived repeating unit is a repeating unit derived from at leastone monomer selected from the group consisting of methyl(meth)acrylate,ethyl(meth)acrylate, propyl(meth)acrylate, and butyl(meth)acrylate. 5.The electrode assembly of claim 3, wherein the acetate group-containingmonomer-derived repeating unit is a repeating unit derived from allylacetate or vinyl acetate.
 6. The electrode assembly of claim 2, whereinthe porous adhesive layer further comprises an inorganic particle, andthe inorganic particle is included in an amount of 70 wt % to 95 wt %based on the total weight of the porous adhesive layer.
 7. The electrodeassembly of claim 2, wherein the porous adhesive layer further comprisesa polyvinylidene fluoride-based binder.
 8. The electrode assembly ofclaim 7, wherein the polyvinylidene fluoride-based binder is at leastone selected from a polyvinylidene fluoride (PVDF) homopolymer,polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidenefluoride-trichloroethylene (PVDF-TCE), and polyvinylidenefluoride-chlorotrifluoroethylene (PVDF-CTFE).
 9. The electrode assemblyof claim 7, wherein a weight ratio of the acryl-based copolymer and thepolyvinylidene fluoride-based binder is 9.9:0.1 to 2.5:7.5.
 10. Theelectrode assembly of claim 1, wherein the electrode assembly has acompression thickness variation ratio of greater than or equal to 10%according to Equation 1:Compression thickness variation ratio (%)=[(Thickness of an electrodeassembly compressed at 20° C.−Thickness of an electrode assemblycompressed at 100° C.)/Thickness of an electrode assembly compressed at20° C]×100   [Equation 1] wherein, in Equation 1, the thickness of anelectrode assembly compressed at 20° C. is a thickness of a centralportion of an electrode assembly including a stackedcathode/separator/anode after compressing it at 20° C. for 1 second to10 seconds, with a pressure of 1 kgf/cm² to 30 kgf/cm² and measuring thethickness in one 1 hour, and the thickness of an electrode assemblycompressed at 100° C. is a thickness of a central portion of theelectrode assembly for 1 second to 10 seconds, with a pressure of 1kgf/cm² to 30 kgf/cm² and measuring the thickness in one 1 hour.
 11. Anelectrochemical battery comprising the electrode assembly of claim 1.12. The electrochemical battery of claim 11, wherein the electrochemicalbattery is a lithium polymer secondary battery or a lithium ion polymersecondary battery.
 13. A method of preparing an electrode assembly,comprising forming a positive active material layer on a cathode currentcollector to prepare a cathode, forming an anode active material layeron a anode current collector to prepare an anode, disposing a separatorbetween the cathode and the anode, and compressing thecathode/separator/anode structure at 20° C. to 110° C. for 1 second to10 seconds with 1 kgf/cm² to 30 kgf/cm².
 14. The method of claim 13,wherein the method further comprises secondarily compressing thestructure at 60° C. to 110° C. for 30 seconds to 180 seconds, with 1kgf/cm² to 30 kgf/cm² after the compressing the structure and injectingan electrolyte.
 15. The method of claim 13, wherein the separatorcomprises a porous substrate and a porous adhesive layer disposed on onesurface or both surfaces of the porous substrate and including anacryl-based copolymer including a (meth)acrylate-based monomer-derivedrepeating unit.
 16. The method of claim 15, wherein the acryl-basedcopolymer further comprises an acetate group-containing monomer-derivedrepeating unit.